The invention relates to the technical field of filtering materials and discloses a preparation method of a filtering membrane material. The preparation method comprises the following steps: dissolving a transition metal salt into a solvent so as to obtain a solution, adding a carbon membrane, uniformly mixing, enabling the components to react in a high-pressure reaction kettle, vacuating the high-pressure reaction kettle, introducing CO2 till the absolute pressure inside the high-pressure reaction kettle is 80-150bar, heating to 35-60 DEG C, performing a reaction, after the reaction is implemented for 0.5-24 hours, releasing CO2 till normal pressure, cooling to room temperature so as to obtain a reaction kettle liquid, drying so as to obtain a precursor carbon membrane, enabling the precursor carbon membrane to react for 2-8 hours at 700-1000 DEG C in a protection atmosphere so as to obtain a transition metal/carbon composite membrane, soaking the membrane into a CS2 solution of sulfur for 1-12 hours, filtering, and drying, thereby obtaining the filtering membrane material. The filtering membrane material prepared by using the method is uniform in transition metal loading, good inconsistency, easy to separate from water, simple to recycle and applicable to industrial production, and has the characteristics of high adsorption efficiency, high adsorption capacity, and the like.